The fourth season of the American television series The Flash, based on the DC Comics character Barry Allen / The Flash, premiered on the CW on October 10, 2017 and ran for 23 episodes until May 22, 2018. The season follows a crime scene investigator with superhuman speed who fights criminals, including others who have also acquired superhuman abilities. It is set in the Arrowverse, sharing continuity with other TV series in the universe, and is a spin-off of Arrow. The season is produced by Berlanti Productions, Warner Brothers Television, and DC Entertainment with Andrew Kreisberg and Todd Helbing as showrunners.
The season was ordered in January 2017, and filming began in July. Grant Gustin plays the role of Barry, and lead actors Candice Patton, Daniel Panabaker, Carlos Valdez, Keynan Lonsdale, Tom Kavanagh and Jesse L. Martin also return from previous seasons, and are joined by Neil Sandilands. The series was renewed for a fifth season on April 2, 2018.